BOVINE SERUM-ALBUMIN POTENTIATES CAFFEINE-INDUCED OR ATP-INDUCED TENSION IN HUMAN SKINNED SKELETAL-MUSCLE FIBERS

Human skinned muscle fibers were used to investigate the effects of bo vine serum albumin (BSA) on the tension/pCa relationship and on the fu nctional properties of the Ca2+-release channel of the sarcoplasmic re ticulum (SR). In both fast- and slow-type fibers, identified by their tension response to pSr 5.0, BSA (0.7-15 mu M) had no effect on the Ca 2+ affinity of the contractile proteins and elicited no tension per se in Ca2+-loaded fibers. In contrast, BSA (>1.0 mu M) potentiated the c affeine-induced tension in Ca2+-loaded fibers, this effect being more intense in slow-type fibers. Thus, BSA reduced the threshold caffeine concentration required for eliciting detectable tension, and increased the amplitude, the rate of rise and the area under the curve of caffe ine-induced tension. BSA also potentiated the tension elicited in Ca2-loaded fibers by low-Mg2+ solutions containing 1.0 mM free ATP. These results suggest that BSA modulates the response of the human skeletal muscle SR Ca2+-release channel to activators such as caffeine and ATP .